1. Field of the Invention
The present invention relates to an apparatus and method for extreme ultraviolet (EUV) spectroscope calibration, and more particularly, to an apparatus and method for EUV spectroscope calibration which may accurately measure a spectrum of EUV light used in EUV exposure technologies and mask inspection technologies.
2. Discussion of Related Art
In general, electromagnetic radiation (also referred to as “soft X-ray”) having a wavelength of approximately 124 nm or less while having extreme ultraviolet (EUV) light, for example, light with a wavelength of approximately 13.5 nm may be used in a photolithography process for forming a very small pitch on a substrate, for example, a silicon wafer.
That is, EUV and X-rays are included in a region having wavelengths shorter than those of visible rays, may improve a measurement resolution by a diffraction limit that is limited by sizes of wavelengths in a precision measurement using light, and may be utilized in micromeasurement or nondestructive inspection related to biotechnologies using excellent transmission characteristics due to extension up to the X-ray region.
In particular, simultaneously, when a light source having excellent coherency can be generated, a variety of applications using the interference and diffraction phenomenon of light are possible. In addition, the EUV and X-rays can maintain the repeatability of entering femto-second laser, and therefore can be used in precision spectroscopy or frequency standard measurement in the EUV and X-ray regions.
Among various methods for generating such EUV and X-rays, a method using a synchrotron may be used. When generating the EUV and X-rays using the synchrotron, it is possible to obtain several different wavelength bands while obtaining a large amount of light with excellent quality, but the facility itself is very large in its size and expensive and therefore a laboratory cannot be simply configured.
As a method for overcoming the above-mentioned problem, a high-order harmonic generation (HHG) method using a high output femto-second pulse laser has been suggested, and therefore coherent EUV and soft X-rays can be generated using a relatively small experimental apparatus.
In the HHG method, by applying a high time-varying electric field to an inert gas such as Ar, Ne, Xe, or the like, electrons are ionized, moved along the trajectory, and then are recombined again, and therefore energy corresponding to a sum of ionization energy and kinetic energy of the electrons may be generated as EUV light or light in X-ray bands.
Conventionally, in order to generate such HHG, it is designed that the inert gas is injected into a gascell and the used inert gas naturally flows out of the gascell.
In addition, EUV may be generated even through lithium, tin, or a semiconductor device as well as the inert gas such as Ar, Ne, Xe, or the like, but a gas may be used as a medium due to HHG using the gascell. This is because a medium for allowing EUV to be generated by HHG using the gascell is only the inert gas due to the current technologies. EUV may be generated through other methods as well as the method of generating EUV using the inert gas.
Meanwhile, according to demands for ultraminiaturization of a semiconductor process for high integration, development up to ArF (193 nm) while passing through G line (436 nm), I line (365 nm), and KrF (248 nm) has been conducted as a light source used in exposure technologies.
Thereafter, new exposure technologies that increase resolution in a semiconductor process of 90 nm or less have been required, ArF immersion exposure technology and double-patterning exposure technology have been developed, and therefore a mass production up to a process of DRAM of 23 nm and NAND flash of 20 nm has been succeeded.
As next generation exposure technologies for overcoming the ArF exposure technology, several technologies have been studied, and research and development on EUV exposure technology among these technologies have been actively conducted worldwide such as reaching a stage of test production by major semiconductor companies, and the like.
Meanwhile, in order to inspect a defect of a mask manufactured by the EUV exposure technology, EUV light is similarly needed. In particular, technology in which the defect of the mask is inspected with the same wavelength as a wavelength used in the exposure technology is referred to as actinic mask inspection technology. In order to generate EUV with the same wavelength as an EUV wavelength used in the exposure technology, an HHG method is needed. In order to check whether the EUV light generated in the HHG method is suitable for a wavelength to be used, a spectrum should be measured using an EUV spectroscope, and in this instance, calibration of the spectroscope should be performed in order to measure the accurate spectrum. As a calibration method of the EUV light, a method using an atomic line which has been traditionally used may be used. Fluorescence lines which are inherent for each inert gas are referred to as atomic lines. Since wavelength values of an atomic line spectrum have been already studied several decades ago and thereby widely known, calibration may be performed on EUV light based on the position of the atomic line spectrum and the wavelength value thereof.
However, in order to obtain energy with an intensity that can be measured by a CCD camera of the spectroscope, energy which is several times higher than energy of a laser used in HHG is needed. Thus, a laser light source that can output energy higher than that of a laser for generating high-order harmonics for EUV is necessarily needed.
Prior Patent Document 1: Korean Patent Registration No. 10-10789135